We remove the title from `errbot` integration documentation so that
all documentations have the same style. See
https://github.com/zulip/python-zulip-api/pull/515 for a similar
change to integrations where the docs live elsewhere in version control.
We also remove the `margin: 0` from the instruction tip because where
the tip is followed by a list, there is no space between the two; this
change doesn't mess up the other places where the tip is used.